diff --git a/src/interfaces/clock.hpp b/src/interfaces/clock.hpp
new file mode 100644
index 0000000..0c355b7
--- /dev/null
+++ b/src/interfaces/clock.hpp
@@ -0,0 +1,22 @@
+#pragma once
+
+#include <chrono>
+
+namespace interfaces
+{
+
+class Clock
+{
+  public:
+    using duration = std::chrono::steady_clock::time_point::duration;
+    using rep = std::chrono::steady_clock::time_point::rep;
+    using period = std::chrono::steady_clock::time_point::period;
+    using time_point = std::chrono::steady_clock::time_point;
+
+    virtual ~Clock() = default;
+
+    virtual time_point now() const noexcept = 0;
+    virtual uint64_t timestamp() const noexcept = 0;
+};
+
+} // namespace interfaces
diff --git a/src/interfaces/metric.hpp b/src/interfaces/metric.hpp
index 3279fd7..62a8f44 100644
--- a/src/interfaces/metric.hpp
+++ b/src/interfaces/metric.hpp
@@ -16,7 +16,7 @@
     virtual ~Metric() = default;
 
     virtual void initialize() = 0;
-    virtual const std::vector<MetricValue>& getReadings() const = 0;
+    virtual std::vector<MetricValue> getReadings() const = 0;
     virtual LabeledMetricParameters dumpConfiguration() const = 0;
 };